In most types of optical data transmission networks, especially in wavelength division multiplex (WDM) networks, it is necessary to stabilize the optical transmission wavelength of the optical transmitters which are usually laser diodes. For this purpose the lasers usually include a thermo-electric cooler and/or a wavelength locker. Known wavelength lockers often include a wavelength discriminator, for example a Fabry-Perot etalon. It is also known to lock the optical center wavelength or optical center frequency of a tunable laser to a desired value using a wavelength (or frequency) locker.
Further, various concepts exist that eliminate a thermo-electric cooler and/or a wavelength locker for each optical transmitter unit within an optical access network, for example within a WDM passive optical network (WDM-PON). For these applications it is known to base the wavelength control on a centralized wavelength locker, which is located either at the optical line termination (OLT) or at a remote node (RN).
However, when using a centralized wavelength locker at the OLT, the tuning information needs to be transmitted from the OLT location to the tunable laser in the optical networking unit (ONU) using a communication channel, which requires additional effort. Furthermore, frequency dithering at multiple distinct dither frequencies is required to distinguish between the ONUs. With a wavelength locker at the RN, the feedback signal is an analog optical signal, which needs to be detected at the ONU, also requiring additional hardware effort. Furthermore, the insertion loss of the (reflective) wavelength locker reduces the power budget of the network. Both methods are not directly applicable for other network scenarios, like metro WDM systems, for which currently no solution exists.